In a Release 10 (Rel-10) Long Term Evolution (LTE) system, for downlink transmission, five reference signals have been defined, i.e., Cell-specific Reference Signal (C-RS), User Equipment-specific Reference Signal (UE-RS, also called as Demodulation-Reference Signal (DM-RS)), Multimedia Broadcast multicast service Single Frequency Network (MBSFN) reference signal, Positioning-Reference Signal (P-RS), and Channel State Information Reference Signal (CRI-RS). The CSI-RS is used for downlink channel measurement and estimation.
FIGS. 1A, 1B and 1C show reference signal patterns supporting the CSI-RS in the LTE system respectively. The reference signal patterns show positions of resources for different reference signals, i.e., positions of Resource Element (REs), to which the different reference signals are mapped, in a Physical Resource Block (PRB).
One reference signal is transmitted through each downlink antenna port. One PRB includes 20 2-port reference signal patterns (as shown in FIG. 1A), 10 4-port reference signal patterns (as shown in FIG. 1B), and 5 8-port reference signal patterns (as shown in FIG. 1C).
As shown in FIGS. 1A, 1B and 1C, the current LTE system may configure 2 ports, 4 ports or 8 ports for the CSI-RS, but it is impossible for the LTE system to support the CSI-RS with more ports.